CHAPTER 8 



Mineral Metabolism and Effect 

 of Salts on Growth 



Mineral elements play a highly important 

 role in the growth of microorganisms. They 

 function both as essential nutrients for cell 

 synthesis and as i-egulatory mechanisms for 

 various transformations that take place in 

 the living systems. The composition of most 

 of the synthetic media used for the growth of 

 actinomycetes bears out this fact. Aside 

 from the required sources of carbon and 

 nitrogen, actinomycetes require phosphorus, 

 sulfur, iron, potassium, magnesium, and cer- 

 tain other inorganic elements. In some cases, 

 as in the production of certain antibiotics, 

 pigments, and \itamins, such elements as 

 potassium, calcium, chlorine, manganese, co- 

 balt, and zinc play most interesting parts in 

 the biochemical reactions involved. 



In most of the earlier studies on the effect 

 of inorganic salts on the growth of actino- 

 mycetes, complex organic media were used. 

 Miinter (1916), for example, used a medium 

 containing blood protein, gelatin, and agar. 

 He still observed that potassium and sodium 

 salts, when used in 5 per cent concentrations, 

 are favorabU' for growth but not for sporu- 

 lation. He further noted that the addition of 

 small amounts of Ca, Ba, and Sr uere fa- 

 vorable for growth and sporulation; higher 

 concentrations were injurious. 



With the recognition of the important lole 

 of actinomycetes as producers of niilibiotics 

 and vitamins, there has Ixhmi an cvvv grow- 

 ing interest in the role of mineral (>lements 



in their nutrition. It was soon established 

 that the great majority of actinomycetes, 

 like other microorganisms, grow at rather 

 low concentrations of salts. Some, however, 

 are able to tolerate very high concentrations. 



Essential Nutrients 



Among the organisms studied most ex- 

 tensively from the point of view of mineral 

 requirements, S. griseus occupies a leading 

 place. A chemically defined medium is more 

 desirable than a complex organic medium 

 for investigating metal re(iuirements for nu- 

 trition and for antibiotic production. 



In a study of the mineral requirements of 

 S. griseus by Chesters and Rolinson, a chem- 

 ically defined medium was used. It was made 

 metal-deficient by treatment with chloro- 

 form solutions of diphenylthiocarbazone at 

 pH 7.3 to remove zinc and copper and with 

 8-hydroxyquinoline at pH 5.2 to remo\'e iron 

 and at 7.3 to remove manganese. Media 

 from which the metals were omitted singly 

 were compared to media in which they were 

 included. When zinc was omitted, the me- 

 dium supported the synthesis of only 75 mg 

 of cvU material per 100 ml of medium. Ad- 

 dition of zinc eciuivalent to 1 part per million 

 of medium permitted maximum growth (550 

 mg/100 ml) and maxinuun streptomycin 

 ])r()ducti()n. Further increases in the con- 

 centrations of zinc resulted in decreased 

 antibiotic production, so that only 50 per 



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